Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/36—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/60—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from the reaction of a mixture of hydroxy carboxylic acids, polycarboxylic acids and polyhydroxy compounds
  • C08G63/605—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from the reaction of a mixture of hydroxy carboxylic acids, polycarboxylic acids and polyhydroxy compounds the hydroxy and carboxylic groups being bound to aromatic rings
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
  • C08J9/06—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent
  • C08J9/10—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent developing nitrogen, the blowing agent being a compound containing a nitrogen-to-nitrogen bond
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/38—Polymers
  • C09K19/3804—Polymers with mesogenic groups in the main chain
  • C09K19/3809—Polyesters; Polyester derivatives, e.g. polyamides
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
  • C08J2367/03—Polyesters derived from dicarboxylic acids and dihydroxy compounds the dicarboxylic acids and dihydroxy compounds having the hydroxy and the carboxyl groups directly linked to aromatic rings

Definitions

• the present invention relates to high performance foams of thermotropic liquid crystal polymers in the form of rigid foamed wholly aromatic polymers which are capable of forming an anisotropic melt phase and which comprise certain essential units. These foams have excellent properties which can be further improved by heat treatment in accordance with the present invention.
• Foamed plastics are very useful in those applications where enhanced mechanical properties such as a high strength to weight ratio is desirable.
• a foam which comprises a rigid foamed wholly aromatic polymer which is capable of forming an anisotropic melt phase and which comprises not less than 10 mole percent of recurring units of the following moiety: wherein at least some of the hydrogen atoms present upon the rings may optionally be replaced by substituents selected from alkyl groups of 1 to 4 carbon atoms, alkoxy groups of 1 to 4 carbon atoms, halogen, phenyl, substituted phenyl and mixtures thereof.
• a method of producing a rigid foam of improved properties which comprises forming a rigid foamed wholly aromatic thermotropic liquid crystal polymer which comprises not less than 10 mole percent of recurring units which include a naphthalene moiety, characterised in that the said foam is subjected to a heat treatment sufficient to increase the melting temperature of the polymer by at least 10°C.
• the invention provides a foam which comprises a wholly aromatic thermotropic liquid crystal 'polymer comprising not less than 10 mole percent of recurring units which include a naphthalene moiety which foam has been subjected to a heat treatment for a period of time and at a temperature sufficient to increase the melting temperature of the polymer by at least 10°C.
• the foams of the invention have excellent thermal, flame and solvent stability and highly desirable mechanical properties; for example high strength.
• Thermotropic liquid crystal polymers are polymers which are liquid crystalline (i.e., anisotropic) in the melt phase. These polymers have been described by various terms, including “liquid crystalline”, “liquid crystal” and “anisotropic". Briefly, the polymers of this class are thought to involve a parallel ordering of the molecular chains. The state wherein the molecules are so ordered is often referred to either as the liquid crystal state of the nematic phase of the liquid crystalline material. These polymers are prepared from monomers which are generally long, flat and fairly rigid along the long axis of the molecule and commonly have chain-extending linkages that are either coaxial or parallel.
• Such polymers readily form liquid crystals (i.e., exhibit anisotropic properties) in the melt phase. Such properties may be confirmed by conventional polarised light techniques whereby crossed polarisers are utilised. More specifically, the anisotropic melt phase may be confirmed by the use of a Leitz polarising microscope at a magnification of 40X with the sample on a Leitz hot stage and under nitrogen atmosphere.
• the polymer is optically anisotropic; i.e., it transmits light when examined between crossed polarisers. Polarised light is transmitted when the sample is optically anisotropic even in the static state.
• thermotropic liquid crystal polymers suitable for use in the present invention are wholly aromatic polymers which are capable of forming an anisotropic melt phase and which comprise mot less than 10 mole percent of recurring units which include a naphthalene moiety, such as a __ 6-oxy-2-naphthoyl,'2,6-dioxynaphthalene and 2,6-dicarboxynaphthalene.
• the wholly aromatic polyesters and wholly aromatic poly(ester-amide)s are considered to be "wholly" aromatic in the sense that each moiety present in the polymer contributes at least one aromatic ring to the polymer backbone.
• wholly aromatic polyesters which can be used in the present invention and which satisfy the above characteristics are disclosed in our U.S. Patents Nos. 4,161,470; 4,219,461 and 4,256,624; and in our U.S. Applications Serial Nos. 128,759, filed March 10, 1980, 128,778, filed March 10, 1980, 169,014, filed July 15, 1980 and 194,196, filed October 6, 1980.
• Exemplary wholly aromatic poly(ester-amide)s are disclosed in our U.S. Application Serial No. 214,557, filed December 9, 1980.
• the wholly aromatic polyester and poly(ester-amide)s disclosed therein typically are capable of forming an anisotropic melt phase at a temperature below approximately 400°C., and preferably below approximately 350°C.
• thermotropic liquid crystal polymer may be further comprised of additonal moieties which contribute at least one aromatic ring to the polymer backbone and which enable the polymer to exhibit anisotropic properties in the melt phase.
• additonal moieties include but are not limited to aromatic diols, aromatic amines, aromatic diacids and aromatic hydroxy acids such as:
• the polymer comprises at least 10 mole percent of recurring units which include a naphthalene moiety, preferably between 10 to 90 mole percent, and more preferably, at least 20 mole percent.
• the wholly aromatic polymers including wholly aromatic polyester and poly(ester-amide)s which are suitable for use in the present invention may be formed by a variety of esterforming techniques whereby organic monomer compounds possessing functional groups which, upon condensation, form the requisite recurring moieties are reacted.
• the functional groups of the organic monomer compounds may be carboxylic acid groups, hydroxyl groups, ester groups, acyloxy groups, acid halides, amine groups, etc.
• the organic monomer compounds may be reacted in the absence of a heat exchange fluid via a melt acidolysis procedure. They, accordingly, may be heated initially to form a melt solution of the reactants with the reaction continuing as said polymer particles are suspended therein.
• a vacuum may be applied to facilitate removal of volatiles formed during the final stage of the condensation (e.g., acetic acid or water).
• the organic monomer reactants from which the wholly aromatic polyesters are derived may be initially provided in a modified form whereby the usual hydroxy groups of such monomers are esterified (i.e., they are provided as lower acyl esters).
• the lower acyl groups preferably have from two to four carbon atoms.
• the acetate esters of organic monomer reactants are provided.
• Representative catalysts which may be optionally employed in either the melt acidolysis procedure or in the slurry procedure of U.S. Patent No. 4,083,829 include dialkyl tin oxide (e.g., dibutyl 'tin oxide), diaryl tin oxide, titanium dioxide, antimony trioxide, alkoxy titanium silicates, titanium alkoxides, alkali and alkaline earh metal salts of carboxylic acids (e.g., zinc acetate), the gaseous acid catalysts such as Lewis acids (e.g., BF3), hydrogen halides (e.g., HC1), etc.
• the quantity of catalyst utilised typically is 0.001 to 1 percent by weight based upon the total monomer weight, and most commonly 0.01 to 0.2 percent by weight.
• the wholly aromatic polymers suitable for use in the present invention tend to be substantially insoluble in common solvents and accordingly are not susceptible to solution processing. As discussed previously, they can be readily processed by common melt processing techniques. Most suitable wholly aromatic polymers are soluble to a small degree (e.g., less than 1 percent.by weight) in pentafluorophenol.
• the wholly aromatic polyesters which are preferred for use in the present invention commonly exhibit a weight average molecular weight of 2,000 to 200,000, and preferably 10,000 to 50,000, and most preferably 20,000 to 25,000.
• the wholly aromatic poly(ester-amide)s which are preferred commonly exhibit a molecular weight of 5000 to 50,000 and preferably 10,000 to 30,000; e.g., 15,000 to 17,000.
• Such molecular weight may be determined by gel permeation chromatography as well as by other standard techniques not involving thesolutioning of the polymer, e.g., by end group determination via infrared spectroscopy on compression moulded films. Alternatively, light scattering techniques in a pentafluorophenol solution may be employed to determine the molecular weight.
• the wholly aromatic polyesters and poly(ester-amide)s additionally commonly exhibit an inherent viscosity (i.e., I.V.) of at least 2.0 dl./g., e.g., 2.0 to 10.0 dl./g., when dissolved in a concentration of 0.1 percent by weight in pentafluorophenol at 60°C.
• I.V. inherent viscosity
• Especially preferred wholly aromatic polymers are those which are disclosed in U.S. Patents 4,161,470, 4,184,996 and 4,256,624.
• the aromatic rings which are included in the polymer backbones of the polymer components may include substitution of at least some of the hydrogen atoms present upon an aromatic ring.
• substituents include alkyl groups of up to four carbon atoms; alkoxy groups having up to four carbon atoms; halogens and additional aromatic rings, such as phenyl and substituted phenyl.
• Preferred halogens include fluorine, chlorine and bromine.
• the foams of the present invention can be formed in any suitable conventional manner such as by extrusion, injection moulding, etc.
• a foam may be formed by screw extrusion by admixing pellets of a thermotropic liquid crystal polymer with a powdered blowing agent and extruding the admixture through an appropriate orifice (e.g., a slit die, etc.).at a temperature greater than the melting temperature of the polymer.
• the blowing agent decomposes at the temperature of extrusion to release a gas such as nitrogen or carbon dioxide within the extruded polymer melt to form the foam.
• the extruded foamed polymer is quenched or cooled by appropriate means such as by forced air.
• extrusion apparatus used is not critical and any suitable apparatus may be used herein. Examples of suitable extrusion apparatus are described in Plastics Engineering Handbook of the Society of the Plastics Industry, Inc., Fourth Edition, edited by Joel Frados, Van Nostrand Reinhold Company (1976), pages 156-203.
• liquid crystal polymer can be extruded at a temperature within the range 250°C. to 350°C. (depending upon the melting temperature of the polymer-) and at a pressure within the range of 100 p.s.i. to 5,000 p.-s.i.
• thermotropic liquid crystal polymers typically exhibit a density of 0.1 to 0.75 gram/cm 3 upon being foamed.
• density of the foamed polymer ranges from 0.3 to 0.75 gram/cm 3 .
• melting point of the foamed thermotropic liquid crystal polymer generally ranges from 250°C. to 320°C. depending upon the specific polymer employed.
• the foamed liquid crystal polymers can be extruded to form a variety of structural articles.
• the liquid crystal polymer can be extruded through a die to form a sheet.
• sheet includes any of various relatively thin, substantially flat structures which may be known in the art as sheets or slabs, etc.
• the liquid crystal polymer can also be extruded through a suitable die to form a rod or tube (e.g., a pipe).
• the foamed thermotropic liquid crystal polymers can also be employed to form moulded structural articles such as by screw injection moulding.
• An admixture of the blowing agent and the pelleted polymer are placed in the hopper of a screw injection moulding apparatus wherein the admixture is heated to above the melting temperature of the polymer and injected into a suitable mould kept at a temperature substantially below the melting temperature of the polymer.
• the polymer is thereafter allowed to cool and is separated from the mould.
• the conditions of temperature and pressure under which the liquid crystal polymer can be moulded are not critical and can easily be determined by one of ordinary skill in the art.
• blowing agents can be employed to produce the foamed polymers.
• suitable blowing agents include but are not limited to those marketed commercially under the trade names Expandex 5 PT (comprised of 5-phenyltetrazole and marketed by Stepan Chemical Co.'), Ficel THT (comprised of trihydrazine triazine and marketed by Fisons Industrial Chemicals), Celogen HT 550 (comprised of a hydrazine derivative and marketed by Uniroyal Chemical) and Kemtec 500 (marketed by Sherwin-Williams Chemicals).
• Such blowing agents generally decompose at a temperature within the range of 240 to 310°C.
• the decomposition of the blowing agent is a function of temperature as well as time. It is important to match the decomposition temperature with the processing temperature of the polymer. If the blowing agent decomposes before the polymer melts sufficiently, poor cell stru.cturemay be attained as well as an unsatisfactory surface appearance.
• the amount of blowing agent required generally ranges from 0.1 percent by weight to several percent depending upon the gas yield of the blowing agent and the desired density reduction.
• the concentration of the blowing agent will range from 0.2 to 0.5 percent by weight.
• the foaming action can be controlled by controlling the temperature and/or the pressure. Control of the foaming action by temperature is more reliable than pressure and the use of a chemical blowing agent is thus preferred.
• fillers and reinforcing agents may also be employed to enhance various characteristics of the foamed polymer.
• suitable reinforcing agents such as glass fibres may be employed to provide reinforcement for the foam.
• Such reinforcing agents generally may be employed in an amount up to 50 percent by weight and preferably from 10 to 50 percent by weight based on the weight of the foam.
• fillers such as pigments, antioxidants and nucleating agents may be added. The amount of such fillers which are generally employed ranges from 0.2 to 10 percent by weight and preferably ranges from 0.5 to 2 percent by weight.
• the foams of the present invention exhibit enhanced mechanical properties due to the orientation of the polymer molecules and the effect of heat treatment. Specifically, the foams exhibit a reduced directional anisotropy in comparison to the unfoamed polymer. Foams having such 'a reduced directional anisotropy are self-reinforcing and have mechanical properties comparable to those of fibre-reinforced polymeric materials.
• the orientation of the polymer molecules around the closed cell bubbles is caused by the biaxial elongational flow field of expanding bubbles during the foaming process.
• the rod-like molecules of liquid crystal polymers can be easily oriented by such a flow field and the biaxial orientation can be retained..
• the foams exhibit enhanced mechanical properties relative to the weight of the foam measured in the transverse direction (TD) in relation to the mechanical properties measured in the machine direction (MD).
• the foams of the present invention also exhibit high flame and thermal stability and excellent solvent and chemical resistance as a result of the properties of the polymer employed therein.
• the polymers employed in the foams of the present invention also exhibit sufficiently high melting temperatures (e.g., above 250°C.) for the foam to be more amenable to heat treatment as discussed below.
• the foams of the present invention also carbonise upon being heated to sufficiently high temperatures which enhances the flame resistance of the foam.
• the mechanical properties of foams produced in accordance with the present invention can be improved still further by subjecting the foams to a heat treatment following formation thereof.
• the heat treatment improves the properties of the foam by increasing the molecular weight of the liquid crystalline polymer and increasing the degree of crystallinity thereof while also increasing the melting temperature of the polymer.
• the foams may be thermally treated in an inert atmosphere (e.g., nitrogen, carbon dioxide, argon, helium) or alternatively, in a flowing oxygen-containing atmosphere (e.g., air).
• an inert atmosphere e.g., nitrogen, carbon dioxide, argon, helium
• a flowing oxygen-containing atmosphere e.g., air
• the use of a non-oxidising atmosphere is preferred to avoid the possibility of thermal degradation.
• the foam may be brought to a temperature 10 to 30°C. below the melting temperature of the foamed liquid crystal polymer, at whir temperature the foam remains a solid object. It is prefer- ble for the temperature of the heat treatment to be as high as possible without equalling or exceeding the melting temperature of the polymer. It is most preferable to increase the temperature of heat treatment gradually in accordance with the increase of the melting temperature of the polymer during heat treatment.
• the duration of the heat treatment will commonly range from a few minutes to a number of days, e.g., from 0.5 to 200 hours, or more.
• the heat treatment is conducted for a time of 1 to 48 hours and typically from 5 to 30 hours.
• the duration of heat treatment varies, depending upon the heat treatment temperature; that is, a shorter treatment time is required as a higher treatment temperature is used.
• the duration of the heat treatment can be shortened for higher melting polymers, since higher heat treatment temperatures can be applied without melting the polymer.
• the heat treatment is conducted under conditions such as to increase the melting temperature of the polymer by at least 10°C.
• the melting temperature of the foamed liquid crystal polymer is increased from 20 to 50°C. as a result of the heat treatment.
• the amount of increase which is obtained. is dependent upon the temperature used in the heat treatment, with higher heat treatment temperatures giving greater increases. It should be noted at this time that reference herein to a temperature below which a specific polymer may exhibit anisotropic properties in the melt phase is intended to refer to the temperature below which the polymer exhibits such properties prior to heat treatment thereof.
• the foam basically being comprised of a skin and a core.
• the skin of the foam is a thih layer (e.g., a few mils thick) consisting of the polymer which possesses a significantly greater density than that exhibited by the core.
• the core comprises substantially the entire volume of the foam (except for the skin) and is of much lower density than the skin.
• the skin is produced during the extrusionofaiinjection moulding process as a result of the flow pattern of the foamed polymer and the influnce of shear forces, etc.
• the thickness of the skin is also related to cooling rates and injection speed, with higher cooling rates and lower injection moulding speeds providing a thicker skin.
• foamed liquid crystal polymers have higher levels of local orientation around the bubbles which facilitates further polymerisation reaction between chain ends.
• by-products of such reaction can diffuse out more easily through the foam.
• thermotropic liquid crystal polymers The chemical resistance also increases with heat treatment and the solubility into pentafluorophenol, one of the rare solvents for thermotropic liquid crystal polymers, continuously decreases with increasing heat treatment time and eventually the material does not dissolve even minimally (such as in amounts of 0.1 percent by weight). Accordingly, reference herein to solvation of the thermotropic liquid crystal polymers is intended to refer to such solvation prior to heat treatment of the foam.
• Pellets of a thermotropic liquid crystal polymer comprised of 40 mole percent of p-oxybenzoyl units and 60 mole percent of 6-oxy-2-naphthoyl units of inherent viscosity 6.0 are admixed with 10 percent by weight of glass fibres as well as various amounts of a powdered Expandex 5-PT blowing agent and injection moulded at a temperature of 280°C. into a mould which is at a temperature of 21°C. to form sample bars.
• the various sample bars produced by the moulding process are examined to determine the tensile, flexural and impact properties of the bars.
• the tensile properties are determined in accordance with standard test ASTM D638, the flexural properties are determined in accordance with ASTM D790 and the impact properties are determined in accordance with ASTM D256.
• Samples 1-5 and Samples 6-10 are formed in moulds of differing size, which accounts for the variation in density reduction attained for the two groups of samples. The results of the examination are set forth in Tables I and II .
• structural articles comprised of foamed wholly aromatic thermotropic liquid crystal polymers of :-he present invention may exhibit a significantly reduced density compared with unfoamed polymers.
• the tensile, flexural and impact properties of the articles comprised of the foamed polymers are of sufficient magnitude to enable the structural articles to be employed successfully.
• Pellets of a thermotropic liquid crystal polymer comprised of 25 mole percent of 6-oxy-2-naphthoyl units and 75 mole percent of p-oxybenzoyl units of inherent viscosity 9.9 are admixed with 0.2 percent by weight of a powdered Kemtec 500 blowing agent and 1.0 percent by weight of talc (a nucleating agent).
• the admixture is extruded at 307°C. from a sheet die of dimensions 10.15 cm x 1.65 mm and taken up at 0.37 meters/minute.
• a Koch static mixer is used just prior to extrusion of the admixture through the die to ensure uniform admixture of the blowing agent and the melt.
• Sample bars are cut from the extruded foamed sheet and examined to determine their tensile properties in both the machine (MD) and transverse (TD) directions according to ASTM D638, Type V. Unfoamed sheets of comparable dimensions of the same polymer produced by the same method are also examined to determine their tensile properties.
• the average density of the foamed sheets is 0.77 gram/cc while the average density of the unfoamed sheets is 1.4 grams/cc.
• the tensile properties of five bars of both foamed and unfoamed samples are determined and averaged to yield composite values which are set forth in Tables III and IV.
• Example 2 demonstrates that the foams of the present invention also exhibit enhanced mechanical properties (relative to the weight of the foam) in the transverse direction (TD) in relation to the mechanical properties measured in the machine direction (MD).
• TD transverse direction
• MD machine direction
• the tensile strength of the foamed polymer measured in the transverse direction substantially equals the corresponding value for the unfoamed sheet (8.68 vs. 10.50) while the initial modulus exceeds the corresponding value for the unfoamed sheet (0.487 vs. 0.420).
• the tensile properties (TD) decrease proportionally less than do the tensile properties (MD) for the foamed polymer in comparison to the corresponding tensile properties for the unfoamed polymer.
• MD tensile properties
• the foamed polymer while its tensileproperties are reduced as a result of being foamed, is actually proportionally stronger in the transverse direction (TD) in comparison to the machine direction (MD) as a result of the foaming.
• the tensile properties become more multi-dimensional (i.e., exhibits a more balanced anisotropy) which permits the foamed polymer to be employed in applications where multi- direction tensile strength is desirable.
• Pellets of a thermotropic liquid crystal polymer comprised of 60 mole percent of p-oxybenzoyl units, 20 mole percent of 2,6-dioxynaphthoyl units and 20 mole percent of terephthoyl units and having an inherent viscosity of 5.4 are screw extruded at 300°C. through a 4 inch (10.2 cm) Killion die to provide several foamed and unfoamed sheet samples.
• a Ficel THT powdered blowing agent 0.5 percent by weight
• 0.1 percent by weight of mineral oil is used to form the foamed samples by admixture with the pellets prior to extrusion.
• the density of the unfoamed samples is 1.4 grams/cc based on the average of five samples.
• the density of the foamed samples is reduced to 0.58 gram/cc which constitutes a 59 percent weight reduction.
• All samples exhibit a melting temperature of 295°C. Certain of the samples are heat treated at 280°C. for 24 hours followed by additional heat treatment at 310°C. for 24 hours whereupon the melting temperature is increased to 341°C. All samples are examined to determine their tensile properties along both the machine (MD) and transverse (TD) directions subsequent to extrusion, and heat treatment according to ASTM D638, Type V. The results of such examination are set forth in Tables V and VI.
• thermotropic liquid crystal polymer foam provides distinct advantages. Specifically, the tensile strength, elongation and initial modulus exhibited by the foamed polymer are all increased significantly as a result of the heat treatment.
• Example 3 also demonstrates that the heat treated foams of the present invention exhibit enhanced mechanical properties (relative to the weight of the foam) in the transverse direction (TD) in relation t& the mechanical properties measured in the machine direction.
• TD tensile strength
• the unfoamed polymers exhibit minor increases in tensile strength (TD) upon being heat treated
• the foamed polymer exhibits a dramatic 65 percent increase in tensile strength (TD) upon being heat treated.
• thermotropic liquid crystal polymer of Example 3 is admixed with 0.2 weight percent of a blowing agent denoted as Kemtec 500 and 1 weight percent of the inorganic filler wollastonite (a nucleating agent).
• Kemtec 500 a blowing agent
• the admixture is screw extruded through a sheet die to provide both foamed and unfoamed sheet samples.
• the density of the foamed sample is 0.61 gram/cc.
• Certain of the samples are also heat treated with the temperature programmed to increase continuously. Specifically, after the samples are dried at 130°C. for 12 hours, the temperature is increased to 260°C. over 4 hours and then to 310°C. over 20 hours.
• Example 4 One of the most striking advantages which is attained by heat treatment of the foams of the present invention is demonstrated by Example 4 and shown by the data in Table VII.
• the effect of the heat treatment depends on molecular orientation; i.e., the more oriented, the greater the effect.
• Table VII the melting temperature increase of the core after heat treatment is greater for the foamed than for the unfoamed articles. This indicates that the orientation of the foam is rather uniform throughout the cross-section and the level of orientation is very high and very close to that of the unfoamed skin.
• the skin of the unfoamed polymer exhibits a greater melting peak increase than does the skin of the foamed polymer
• the lower increase in the melting peak of the foamed skin is not a disadvantage due to the fact that the skin volume comprises a relatively small proportion of the total foam volume.
• Pellets of a thermotropic liquid crystal polymer comprised of 75 mole percent of p-oxybenzoyl moieties and 25 mole percent of 6-oxy-2-naphthoyl moieties and having an inherent viscosity of 9.9 are screw extruded through a 4 inch (10.2 cm) Killion die to provide both foamed and unfoamed sheet samples.
• a Celogen HT 550 (0.1 percent by weight) and Kemtee 500 (0.2 percent by weight) blowing agent are used to form the foamed samples by admixture with the pellets prior to extrusion. All samples (foamed and unfoamed) exhibit a melting temperature of 301°C.
• the melting temperature of the core of the foamed sheets can be increased to a greater extent than is the melting temperature of the core of the unfoamed sheets, thus demonstrating that the foamed polymer is more amenable to heat treatment than the unfoamed polymer.

Landscapes

• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Crystallography & Structural Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Polyesters Or Polycarbonates (AREA)

Applications Claiming Priority (4)

Publications (3)

Family

ID=26961690

Family Applications (1)

Country Status (3)

Cited By (5)

Citations (8)

• 1982
  • 1982-06-30 CA CA000406327A patent/CA1194649A/en not_active Expired
  • 1982-07-09 DE DE8282303608T patent/DE3277305D1/de not_active Expired
  • 1982-07-09 EP EP19820303608 patent/EP0070658B1/de not_active Expired

Patent Citations (8)

Also Published As

Similar Documents

Legal Events